It is our common understanding that in dilute aqueous solution the salts exist in two different states, soluble or insoluble (homogeneous or macrophase separation). When the soluble ions become larger in size, i.e., ~1-5 nm (macroions), their behaviors might become more complicated, due to the noticable counterion association and the consequent counterion-mediated attraction. We recently identified two other phases in the aqueous solutions of nanoscale anionic clusters: gel and coacervate. The gel phase was observed in both highly charged macroions, represented by the uranyl peroxide macroanions {U60}60- and {U24pP12}48- synthesized by Peter Burns' group; and weakly charged metal oxide macroions {Mo7O24}6- from Hongying Zang's group. In both cases multivalent countercations are needed. For the highly charged clusters, the counterion-mediated attraction leads to their formation of 2-D sheets (high charge cluster case). Due to the strong attraction from the multivalent cations, the 2-D sheets cannot bend and enclose to form the well-studied blackberry type structures, but stay as standalone sheets in solution. Their large excluded volume leads to the gelation in low concentrations (0.5 mg/mL), similar tot he graphene gelation process. For lowly charged clusters, the same electrostatic interaction leads to 1-D linear chains and consequently form gels similar to the gelation of polymer chains. The coacervate phase covers a broad range in the phase diagram and is also fascinating because its formation mechanism is different from the commonly known coacervates formed by the strong interaction between positively and negatively charged polyelectrolytes. Positively charged macroions are missing from the current system. A new model is presented to explain their formation and features. Overall, we demonstrate that when soluble ions reach the scale of nanometer scale, they would possess very unique and complex features such as multiple macrophase transitions.

Macrophase separations in dilute aqueous solutions of molecular clusters with the gel and coacervate phases

Where thousands of chemistry professionals meet to share ideas and advance scientific and technical knowledge. Spring 2023 abstracts, posters, and presentations will launch at the end of March.

ACS Spring 2023

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.